#include <iostream>
#include <vector>  
using namespace std;

int main() {
    int w,h,count = 0;
    cin >> w >> h;

    vector<vector<int>> a;
    a.resize(w);
    for(auto& e : a)
    {
        e.resize(h,1);
    }

    for(int i = 0; i < w;i++)
    {
        for(int j = 0;j < h; j++)
        {
            if(a[i][j] == 1)
            {
                count++;
                if(i+2 < w)
                {
                    a[i+2][j] = 0;
                }
                if(j+2 < h)
                {
                    a[i][j+2] = 0;
                }
            }
        }
    }
    cout << count << endl;
    
}


